1. Field of the Invention (Technical Field)
The present invention relates to a high-density, high-resolution array of light valves that can be selectively activated by low induced voltages to alter a light beam passing through the array. The present invention also relates to a process for manufacturing such a high density light valve array using semiconductor-type processing equipment and techniques.
2. Background Art
In much the same way that single crystal silicon can be processed to selectively permit or block the passage of electrons (conductivity), an electro-optic material, such as lanthanum modified lead zirconate titanate (PLZT), can be processed to permit or block the passage of a beam of light by application of an electric field, between two electrodes in the material, perpendicular to the direction of the light beam. In both cases, the starting material is a wafer which is cut from a cylindrical boule and then subjected to processing steps that build microstructures on one side of the wafer.
The application of an electric field induces birefringence in a transparent PLZT material. Bi-refringence is a rotation in the plane of polarization within the PLZT material. This phenomenon is referred to as the Kerr effect. The configuration of two oppositely charged electrodes separated by an electro-optic material, such as PLZT, and sandwiched between two polarizers is well known in the art and referred to as a Kerr cell. Once induced, the bi-refringence in the electro-optic material of a Kerr cell can lower, or increase light transmission through the cell. In applications where electrode spacing within the PLZT is very small, selective electronic birefringent addressing can be used to create a small high-resolution display or high quality image, which can be directly viewed, or projected and enlarged.
Reduced electrode spacing within the PLZT material is particularly desirable as it offers benefits of reduced activation voltage, reduced picture cell (pixel) size, and higher image resolution. Higher electrode density also induces the problems of increased manufacturing costs and complexity, and difficulty in connecting the array electrodes to those of other arrays or to controlling electronics, such as printed circuit boards.
Reduced electrode spacing has been achieved in the prior art predominately through the use of mechanical grooving of the PLZT substrate, longitudinal (parallel to light beam) activation of the PLZT, and/or stenciling techniques for placement of the electrodes within the grooves. However, such manufacturing techniques limit the number of light valves, or picture cells (pixels), to numbers on the order of 25 to 100 pixels per linear inch. Pixel dimensions on the order of those disclosed in the prior art also suffer the disadvantages of high activation voltages (100 to 500 VDC), cumbersome requirements for electrical contact designs, and very high lead counts.
The transversely activated electro-optic light valve array in U.S. Pat. No. 5,198,920, co-authored by the inventor of the present invention, discloses means to overcome the switching time, voltage, and addressing shortcomings of the prior art Gobeli et al. '920, discloses a two-dimensional array of Kerr cell pixels defined in an electro-optic material, such as PLZT, between adjacent electrodes deposited onto the substrate. The array may be addressed optically or electronically to generate an electric field in the electro-optic material. Pixel densities as high as 1000 pixels per linear inch are possible using the technology disclosed in Gobeli et al. '920.
The present invention constitutes a significant improvement over this prior aft patent by the use of semiconductor processing technology to further increase pixel density and reduce activation voltage. It further offers the advantage of increased light transmission (brightness) through the PLZT material by a reduction in surface area of the PLZT required for the non-transmissive electrodes.